1. Field of the Invention
The present invention relates principally to a hydraulic system for controlling the position of seeding or tillage tools used for agricultural operations and, more particularly, for no-tillage seeding or planting of cereal crops and others. Soil conditions are more particular in no-tillage seeding due to the absence of soil leveling by tillage. The present invention also relates to a system having a carrying mode and a ground following mode.
2. Description of the Prior Art
No-tillage seeding requires considerable seeding tool downpressure to penetrate residue-covered soil and to open a furrow in sometimes hard soils to ensure proper seeding depth. Most of the available seeders use a mechanical spring to transfer weight from the seeder frame to individual seeding units. The force applied by these springs is not constant due to the compression and extension of the springs when the seeding tools encounter different soil surface elevations. The seeding tool penetration into soil and depth control is thus unreliable due to such varying downward forces which are applied. Manual adjustment of each spring has to be done to obtain the right downpressure force on each seeding tool for given surface and soil conditions. Raising and lowering of the seeding units in this case can only be accomplished by either moving the seeder frame or by operating a common seeding tool bar linked to the frame. These systems require considerable space on the seeder and performance is highly dependent on field surface leveling conditions.
U.S. Pat. No. 4,648,466 issued to Baker et al. on Mar. 10, 1987 describes a system to hydraulically control seeding tools from a tractor. Two hydraulic accumulators provide pressure on the seeding tool's hydraulic cylinders when the seeder is in operation. The first accumulator is always at a same pressure as the seeding tool's hydraulic cylinders, while the second accumulator is used as a cushioning system to prevent excess pressure in the hydraulic lines. No provision is made to detect pressure variations when the system shifts from a tractor mode for lifting the seeding tool to an accumulator mode used during the actual seeding operation. Accumulator pressure can thus vary due to the pressure differential when raising and lowering the seeding tool. Correction of the floating system pressure has to be made manually with a second tractor directional valve. Furthermore, this hydraulic control system requires one hydraulic cylinder for each seeding tool.
U.S. Pat. No. 5,065,681 issued to Hadley on Nov. 19, 1991 discloses a hydraulic downpressure structure for an implement having multiple ground engaging tools, wherein the pressure is maintained constant on the ground engaging tools by way of a hydraulic system accompanied by a spring 82. Such a spring will result in a variable force on the ground engaging tool in view of the ground surface irregularities.
U.S. Pat. No. 4,333,534 issued on Jun. 8, 1982 to Swanson et al. discloses a pivoted mechanical structure and a passive cylinder to cause the wheels 27, 32 to follow the soil surface while maintaining constant the depth of the disks 31. The force on the tool bars 10 issues from the contact of these wheels with the ground rather than from the penetration of the disks 31 in the soil.
U.S. Pat. No. 4,506,609 issued on Mar. 26, 1985 to Fuss et al. uses two independent hydraulic systems for the raising and lowering of the seeders and for the depth control of these seeders which thus can float along the profile of the terrain. No interactive control of the force applied by the system on the seeders is provided.
U.S. Pat. Nos. 2,750,862 issued to Garmager on Jun. 19, 1956, No. 2,964,113 issued to Presnell et al. on Dec. 13, 1960 and No. 4,431,061 issued on Feb. 14, 1984 to White all disclose passive hydraulic systems for maintaining a farm implement in place.
U.S. Pat. No. 1,808,759 issued to Bickerton on Jun. 9, 1931 teaches a primitive system for raising an agricultural implement and of manually controlled variable pressurization.
U.S. Pat. No. 4,291,638 issued to Renwick on Sep. 29, 1981 describes an agricultural implement and a passive hydraulic-mechanical system for adjusting the force acting on the springs of this implement. As in the previous patent to Bickerton, there is no interactive control of this force in Renwick.
U.S. Pat. Nos. 4,209,067 issued on Jun. 24, 1980, No. 4,353,423 issued on Oct. 12, 1982 and No. 4,422,511 issued on Dec. 27, 1983, all in the name of Poggemiller et al., all teach the use of fully extended cylinders to which are mounted various farming implements and which act as a protection mechanism against breakage which could result from irregularities in the soil surface such as rocks.
U.S. Pat. No. 4,913,070 issued on Apr. 3, 1990 to Morrison, Jr. discloses an apparatus for controlling the depth of soil penetration of an agricultural ground contact implement, wherein there is provided a continuous dynamic regulating of an adjustable downpressure system in response to translocational movement of a depth gauging wheel.
A major improvement to hydraulic pressure systems for seeders brought about by the present invention results in the correction of these disadvantages. As well, the improvement includes the possibility of coupling two seeding tools to a same hydraulic cylinder by means of a double linkage system, thereby reducing cost. The present improved hydraulic force control system allows for significantly more precise no-tillage seeding for most soil conditions.